Many types of weapons (such as rifles) have weapon sights that allow the weapon's user to view a target within a scene and align the weapon relative to the target, e.g., to select a bullet impact point. A typical weapon sight includes a cross-hair reticle. The weapon sight is adjusted (“aligned”) so that the cross-hairs match the desired bullet impact point for a given target distance. The typical weapon sight is configured to mount to a military standard rail mount (“rail”) (e.g., MIL-STD 1913) that runs along the top and/or side of the weapon (forend and barrel).
A “night sight” weapon sight is used for night vision, while a “day sight” is used for day vision. Some weapon sights have combined night-vision and day-vision capability. Night sights can be configured to clip on and clip off of a weapon as needed.
In some cases, it is desirable to view a scene in a manner that combines images obtained at different wavelength bands. Such images are called “multi-spectral images” and require a weapon sight configured to handle the different wavelength bands. Unfortunately, conventional optical systems designed to handle multiple wavelength bands tend to be complex and bulky, while a weapon sight needs to be simple and compact.